The present invention relates to a system for heating the intake pipe of an internal combustion engine by the heat produced by the combustion of the air-fuel mixture in a combustion equipment in order to facilitate the complete combustion of the air-fuel mixture charged into the cylinders or combustion chambers of the engine.
There has been devised and demonstrated the prior art intake pipe or manifold heating system of the type in which the portion of the intake manifold or pipe at the downstream of the carburetor is heated by the exhaust gas or water recirculated from the radiator. But this system cannot supply the sufficient heat for vaporizing the fuel particles flowing from the carburetor. Especially when the cold engine is started so that the temperature of the exhaust gases or cooling water is low, some fuel particles are charged into the cylinders or combustion chambers, resulting in the undesired air-fuel mixture distribution among the cylinders or combustion chambers. Furthermore, this prior art system has a defect that the smooth engine operation is adversely affected when the engine is accelerated or decelerated. A further defect is that the rich air-fuel mixture must be charged in order to ensure the smooth engine operation, resulting in the emission of a relatively large quantity of pollutants.
In order to overcome the above defects, there has been devised and demonstrated a heating system of the type in which the intake manifold or pipe is heated by the heat produced by the combustion of the air-fuel mixture in a combustion equipment. However, this prior art system also has a defect that the heat or combustion gases in proportion to the air-fuel mixture produced in the carburetor cannot be attained so that there is a danger that the intake manifold or pipe is overheated or is not sufficiently heated. That is, even when the intake manifold or pipe is heated in excess of a certain temperature, the evaporation of the fuel is conversely adversely affected. Therefore, the result is the waste of the fuel in the combustion equipment. Furthermore there is a danger that the intake manifold or pipe is locally melted. On the other hand, when the intake manifold or pipe is not sufficiently heated, the atomization and evaporation of the fuel is adversely affected.
In order to overcome the above defects, the same inventor proposed a heating system of the type in which the air discharged from an air pump for supplying the secondary air to an exhaust gas purifying device is supplied to the combustion equipment as the combustion air and an air flow control valve is inserted in an air supply line interconnecting the air pump and the combustion equipment, whereby the temperature of the intake manifold or pipe may be maintained at the optimum level by controlling the flow rate of the air by the air flow control valve. However, this sytem has a defect that the temperature rising rate of the intake manifold or pipe is relatively low especially when the engine is started at low temperatures.